Well, its not definitive but so far I am tending towards
Something with sdl2
being in the AUR and have the fcitx5
build depend and the use of pamac (repo+aur).

Is an input method required by
sdl2
andsdl3
now, where it was not required prior to 2025.02.16 update?
Nope. Neither sdl2-compat
nor sdl3
require fcitx5
.
Even if you reverted to sdl2
from the AUR fcitx5
would still not be required except to build the package.
( Aside from not exhibiting the issue of source ‘confusion’, every competent AUR helper provides ways to automatically remove build depends after transactions. Let alone removing the AUR from the equation and using pacman
alone - I doubt would have created this scenario. [Would be an interesting test if someone uses backups. ])

And if I choose to “defy” such mandate, is it safe for me to remove
fcitx5
?
I dont know why you are so eager to paint this with overtures to authoritarianism.
Its just a package exchange.
( even if an undesirable one )
But yes, you can safely remove fcitx5 and related packages … as shown by the dependencies.